In electronic instruments, a flexible printing circuit board (sometimes referred to as “FPC”) is widely utilized. In such an FPC, an adhesive is used in (1) a step of adhering and laminating a conductive metal foil (for example, copper foils and aluminum foils) on a heat-resistant substrate (for example, polyimide-made substrates and polyamide-made substrates) to prepare FPC or (2) a step of adhering FPC to a reinforcing plate (such as aluminum plates, stainless steel plates, and polyimide plates). As such an adhesive to be used in adhesion of FPC, there have hitherto been widely utilized nitrile rubber (NBR)/epoxy resin based adhesives, acrylic rubber/epoxy resin based adhesives, and acrylic rubber/phenol resin based adhesives (see U.S. Pat. Nos. 3,822,175 and 3,900,662).
However, in adhesives containing an epoxy resin, such as nitrile rubber (NBR)/epoxy resin based adhesives and acrylic rubber/epoxy resin based adhesives, though their adhesive strength is thoroughly satisfactory, since the adhesiveness is revealed by a chemical reaction of the epoxy resin, there is encountered a problem that the storage stability as an adhesive is low.
Also, in recent years, FPC has been used in precision electronic parts (instruments). Depending upon applications of FPC, in order to prevent contact failure from occurring, it is demanded to exclude silicone based materials even in adhesive tapes or sheets to be used in adhesion with respect to FPC.